Because of its complexity, chess offers limitless possibilities. After just three moves, there are over 9,000,000 possible configurations of the board.
Mathematician Claude Shannon calculated the total number of possible board configurations in a game. The result is called the Shannon Number in his honor. He assumed an average of about 1,000 possibilities for a pair of moves consisting of a move for White followed by a move for Black, and a typical game lasting about 40 such pairs of moves.
The conservative lower bound number he came up with is 10120 (1 novemtrigintillion) possibilities.
Curiously, chess is not the most complicated game. Read about the game that has that distinction here.